Contact and non-contact slot nozzle dies for applying uniform layers of adhesive material to planar surfaces of a substrate are known in the art, particularly in the application of adhesives to carton flaps and moving webs, for example. Several known contact and non-contact slot nozzle dies for use with adhesive dispensers include U.S. Pat. Nos. 4,774,109 and 5,389,151, both assigned to Nordson Corporation of Westlake, Ohio, assignee of the present invention. As the terminology would imply, "contact" slot nozzle dies are adapted to contact the substrate during application of the adhesive material, while "non-contact" slot nozzle dies, on the other hand, have a defined spacing or gap between the elongated slot outlet of the die and the moving substrate during the adhesive application process.
In the "contact" application of adhesive material to a substrate, a die head structure is typically mounted to an adhesive dispenser and includes an adhesive channel which terminates in an elongated slot outlet at a lower end of the contact die. The contact die generally includes a back plate, an intermediate shim, and a front plate which are fastened to an adapter mounted to the adhesive dispenser. The intermediate shim typically includes a cut-out region which defines an adhesive channel between the back and front plates of the contact die. The adhesive channel terminates in the elongated slot outlet which is disposed generally transversely to the direction of travel of the moving substrate. The contact die has lower surfaces which lie in a horizontal plane to contact the planar surface of the substrate during the adhesive application process. The back plate of the contact die serves as a doctor blade to remove excess adhesive from the planar surface of the substrate to achieve a uniform layer of adhesive on the substrate.
While "contact" slot nozzle dies have been used widely in the past for applying uniform layers of hot melt adhesive to planar surfaces of a substrate, such as to carton flaps and moving webs, there is a need for a die head structure which is suitable for contact application of adhesive to non-planar, contoured surfaces of a substrate. Additionally, there is a need for a contact die head which is adapted to simultaneously apply uniform layers of adhesive to multiple non-coplanar surfaces of a substrate. Moreover, there is a need for a contact die head structure which accommodates for flexibility in the substrate during the contact application of adhesive.
In the automobile manufacturing industry, for example, there is a need for a contact die structure which is adapted to apply hot melt adhesive layers to contoured surfaces of an automobile weatherstrip. As shown in FIG. 1, a prior art process for the continuous in-line manufacture and flocking of automobile weatherstrips is shown generally as numeral 10. As is know in the art, automobile weatherstrips are designed to be attached around the inside perimeter of a door window frame for providing an impervious barrier or seal between the frame and the window glass. Weatherstrips are generally made of cured rubber material and have a particular configuration or profile for attachment about the perimeter of the door window frame. It is customary in the industry to apply flocking material to surfaces of the weatherstrip which contact the window glass to reduce undesirable friction between the contacting surfaces. The flocking material also serves a cosmetic purpose to provide a decorative surface to the weatherstrip which is partially visible from inside the passenger cabin.
In the known prior art process 10 of FIG. 1, raw material is fed into an extruder 12 which has a die outlet configured to provide the desired profile of the weatherstrip. The raw material is heated within the extruder 12 and forced under pressure through the die outlet. The heated and cured rubber weatherstrip is then conveyed to a water bath 14 where it is cooled before being transported to an adhesive application booth 16.
Adhesive application booth 16 is conventionally used in the in-line manufacturing process 10 to apply solvent-based adhesives to surfaces of the weatherstrip which are to be flocked. Typically, the solvent-based adhesive, such as Lord Corporation's "Flock-Loc" Product No. 7615, has a low flash point so a Halon exhaust system, shown generally as 18, is required to evacuate hazardous solvent effluents 20 from the booth. The solvent-based adhesive is typically dripped (at room temperature) onto selected surfaces of the moving weatherstrip, while brushes or other flexible-type applicators are used to spread the adhesive into layers having desired width and thickness. An exit conveyor 22 is provided downstream of the adhesive booth 16 to transport the weatherstrip to a conventional flocking booth 24 where flocking fibers are applied to the adhesively coated surfaces of the weatherstrip. After the flocking step, the weatherstrip is typically cooled through a cooling conveyor and water bath 26 before being passed downstream for further processing and installation.
It will be appreciated that the application of solvent-based adhesives to the weatherstrip in the prior art process has several disadvantages. The solvent-based adhesives typically have a low viscosity so it is difficult to effectively control application of the adhesive in a uniform layer to selected surfaces of the weatherstrip. Additionally, the brush or flexible-type applicators used to spread the adhesive generally require extensive manual set-up and adjustment in clamp fixtures, and do not provide adequate sharp edge control of the adhesive layers. Moreover, the hazardous nature of the solvent-based flocking adhesives presents environmental and operational concerns in the automobile weatherstrip manufacturing process. It will be appreciated by those skilled in the art that uniformity of the adhesive layers on the weatherstrip is critical in the flocking operation for achieving flocked surfaces which have complete coverage with sharply defined edges.
Accordingly, it is an objective of the present invention to provide an improved adhesive dispensing system which eliminates the use of solvent-based adhesives in the process of manufacturing and flocking automobile weatherstrips. It is also an objective of the present invention to provide an improved adhesive dispensing system which applies more uniform layers of adhesive on selected surfaces of the weatherstrip, with sharper edge control. Moreover, it is also an objective of the present invention to provide an improved adhesive dispensing system which is readily interchangeable to accommodate for different profiles of weatherstrips which may be encountered in the in-line manufacturing and flocking process.